William Aird
William Aird

@WilliamAird4

4 Tweets 62 reads Feb 01, 2023
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#GI #GIbleed #urea
Elevated BUN: creatinine ratio favors UPPER over lower GI bleed.
Why?
1) Hb in stomach --> amino acids (aa).
2) aa absorbed by small intestine.
3) aa transported and taken up by liver.
4) In the liver, aa undergo deamination, leading to release of NH3.
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5) NH3 (aka ammonia) is converted to urea by the urea cycle, leading to elevated blood urea levels.
6) Meantime, creatinine is not influenced by the protein/aa bolus.
7) Thus, BUN/creatinine ratio is increased.
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So why does blood cause this bump in urea and increase in BUN/creatinine ratio, whereas a steak dinner does not?
Because blood has poor BIOLOGICAL VALIUE (the protein is poorly utilized by the body).
The LOWER the biological value of a protein, the HIGHER the urea.

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